Infrared computing recorder



April 4, 1953 w. JACKSON, JR, ETAL 2,634,908

INFRARED COMPUTING RECORDER Filed April 1, 1950 INVENTORS. WARREN ,JACKSONJR.

ROBERT W. FOREMAN THEIR ATTORNEYS.

Patented Apr. 14, 1953 INFRARED COMPUTING RECORDER Warren Jackson, Jr., East Cleveland, and Robert W. Foreman, Cleveland, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio Application April 1, 1950, Serial No. 153,446

7 Claims. 1

The present invention relates to computers and more particularly to new and improved computing apparatus for determining the ratio between two quantities, either or both of which may be variables. More specifically, it has to do with new and improved computing apparatus for recording values such as the percentage transmission of radiant energy through a sample substance over a selected range of wave lengths, for "example, although it is not limited to such use.

' In quantitative analysis, a determination of the infra-red absorption data of a sample is often required. Usually, such data are expressed in terms of the percentage transmission of infrared radiation through the sample over a. specified range of "wave lengths. With the single beam type of recording infrared spectrophotometer, it is customary to record first the transmission curve for an empty blank cell and then to record the curve for a cell filled with a sample over the same range of wave lengths. The ratio of the transmission through the sample cell to that through the blank cell times 100 is the percent transmission through the sample alone.

. The point-by-point computation of the ratio at each wave length for which a percentage transmission value is desired is a tedious and slow procedure. For this reason, semi-automatic means have been devised for computing percentage transmission values. In one device of this type, percentage transmission curves for the empty cell and for the cell filled with a sample are recorded "on the same chart. The chart is then placed in another instrument and the curves are traced simultaneously by hand with two pointers placed on a single track. At each wave length, one of the pointers selects a voltage proportional to the -percentage transmission for the empty cell and applies it to the other pointer which impresses it across a resistance proportional to the percentage transmission for the cell filled with the sample. The current then flowing in the resistor is directly proportional to the percentage transmission for the sample alone.

While the foregoing semi-automatic apparatus eliminates the necessity for point-by-point com- .putation,-it requires considerable ambidexterity for operation,.in that the blank and the sample curves must be followed simultaneously by manually operated pointers while the recorder chart is in motion. It is an object of the invention, accordin ly, to provide new and improved ratio or percentage determining computer apparatus which is rapid yet simple and highly effective in operation.

Another object of the invention is to provide new and improved computer apparatus of the above character which obviates the need for manually tracing simultaneously two curves representing values of the two quantities entering into the ratio to be determined.

A further object of the invention is to provide new and improved computer apparatus in which the percentage transmission of radiant energy through a sample over a specified range of wave lengths may be determined while the same is be ing examined by a spectrophotometer or the like for the first time.

Still another object of the invention is to provide new and improved computer apparatus which may be combined with spectrophotometric apparatus or the like in such fashion as to permit operation of the latter either normally or in conjunction with the computer apparatus as desired.

These and other objects are attained in the determination of infrared absorption data, for example, by first recording on a chart a curve of percentage transmission through the blank cell. The chart is then turned back to its starting position and the recording of the curve of the percentage transmission through the cell filled with the sample is begun. Simultaneously, the blank cell transmission curve is traced with a manually operated pointer. The movements of the pointer produce corresponding variations in the magnitude of a voltage which energizes a self-balancing potentiometer device. The potentiometer slider is automatically adjusted so that the voltage output therefrom is always equal to the value of voltage corresponding to the sample filled cell percentage transmission at every instant. The curve recorded on the chart by a marking device linked to the potentiometer slider is, therefore, a curve of the percentage transmission through the sample alone.

The invention may be better understood from the following detailed description of a representative embodiment, taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of an electrical computer circuit constructed according to the present invention; and I Fig. 2 illustrates mechanical details of part of El e rlecorder apparatus used in the circuit of While the computer of the invention may be adapted for a Wide variety of uses, it will be described herein, by way of example, as applied to the determination of the percentage transmission of infrared radiation through a sample over a specified range of wave lengths.

As shown in Fig. 1, typical computer apparatus for determining the infrared spectra of a sample in quantitative analysis may comprise a suitable infrared spectrophotometer Hi such as the Beckman model IR-Z, for example, and a self-balancing potentiometer ll of conventional type. The potentiometer ii may comprise, for example, a resistance wire l3 engaged by-aslider I i driven by a motor 15. The motor i is energized by a suitable amplifier l2 through the conductors lb. The slider It carries an inking pen ll (Fig. 2) which is adapted to record a trace i8 'on a chart l9 mounted on suitable rollers in 'the recorder H.

The construction of the spectrophotometer H3 is well known and it will be'necessarytodescribe it only briefly. As shown in Fig. 1, light from a Nernst glower 69 is interrupted say ten times a second by a rotating shutter Si passes through a rock salt window 52 and is focussed by a condensing mirror 53, forming an image of the source in the focal plane of a concave rock salt lens 65. The collimated beam passes througha filter slide and shutter =65 and a liquid cell compartment 66. Aliens 5] converges the beam through a gas cell compartment 623 and a lens 59, forming an image of the source on an upper entrance slit in a diaphragm 7E3. Lightiromthe slit in the diaphragm 10.15 collimated by a spherical mirror ii and dispersed by aprism 12 from which it passes to a rotatable Littrow mirror '33 which is adapted to herotated by amotor Hi for-automatic continuous spectral scanning. Light reflected by the rctatable mirror 33 is dispersed a second time by the prism 12 'and-focussed by the lens H on the plane of an exit slit in thediaphragm iii, which lies just below the entrance slit therein. The beam is directed by a plane mirror against a condensing mirror 16 which focusses an image of the exit slit on a photosensitive device TI. The output of the photosensitive device ll passes through an ,A. C. amplifier l8 and a rectifier and D. C, amplifier l9, one terminal of which is connected by a conductor :88 to the slider it on the resistance wire lit. The other terminal of the rectifier and amplifier i9 is connected to one terminal of the amplifier l2, the other terminal of which is connected by a-conductor 82 to the lower end of the resistance-l3.

When the motor is in the spectrophotometer .ID is energized, it rotates the mirror 13 causing adjacent portions of the radiant energy spectrum in the beam of light passing through either the liquid cell compartment 55 or thergas cell comartment to impinge successively on the photosensitive device ll. This produces an output at the terminals of the rectifier .and amplifier l9 which is ;a function of the radiant energy transmission at adjacent points in the spectrum through liquid or gas contained in the compartment B6 or E3, respectively.

The voltage input to the amplifier i2 is the difference vbetween the potential at the slider M with respect to the conductor 2 5 and the voltage output from the spectrophotometer it]. As is well knownin the art, if the resultant potential difierence in the input .circuitito the amplifier i2 is zero, the motor is remainsat rest. However, if the resultant potential 'difierence is not zero, but has-a positive or negative value, the motor 15 is energized and moves the slider It in the proper direction to reduce that potential difference to zero.

According to the invention, the voltage applied to the resistance wire [3 in the recorder H is adapted to be adjusted manually to be proportional to the percentage transmission through the blank cell over the same range of wave lengths as for the sample curve. A typical electrical circuit for accomplishing this result comprises a source of constant voltage such as a battery 2%, for example, one terminal of which is connected by a conductor 2| to a terminal 22 on a triple pole double-throw switch '23 of '-;conventional type, and the other xterminal co'f :which s. connected by the conductors 24 and 25 to one ter- '-minal cc of a precision resistor 26. The other terminal 6! .of the resistor 26 is connected in series with a variable resistance 2! to a switch blade 2-3 on-the :switch 23.

The precision resistor 26 is engaged by a contact 29 which .is-connected in series with a resistor to to a switch blade 3| on the switch 23. Theswitch blade 3| is adapted to engage a contact '32 which is connected by a conductor 33 to one terminal of the resistance 13 in the recorder H, the other terminal of which is connected by the conductors 2'4 and25 to theterminal-filllofthe precision resistor 2-5.

The switch 23 also carries a switch :blade :35 which is adapted to engage a contact '35 connected by a conductor 36 in series with asuitable source of voltagesuch as a dry cell :31 and aresistor38 to the conductor .33.

From the foregoing, it will :be understood that when theswitch 23 is thrown to the llefteha-nd position, the resistor -l 3-in the recorder Ll willbe energized by :the dry cell .3? through theres-istor 3 3. The switch-23 is thrown to .thisposition when it is desired to record percentage transmission curves in the usual-manner. However, whenzthe switch 23 is thrown to the right-hand position, the resistor is in the recorder M is .energizedby a manually adjustable voltage from the precision resistor 25.

Mechanism suitable for manuallyadjusti-ng the resistor 26 relatively to the lcontactzil issliown in greater detail in Fig. 2. The precision ,resister 25 is mounted on a disc-like member .39 carried by a pulley til-mounted on abracket "4| secured to the casing of the recorder .H. The disc-like member .39 is adapted to be rotated by means .ofa knob 52 mounted on the bracket 41 which carries a gear 43 engaging :a gear 44 mounted on the disc-like member 39..

Mounted on the pulley All and-.on-an idler pulley 2 5 secured on the recorder casingis a continuous belt .or cord ll to which is .securedajpointer 48 slidably mounted .on theusual :glass tear strip 49 on the recorder l i. It will be understood that .by adjusting the knob '52, the pointer '48 may be moved from'side to side as re uired toiollow-a curve 5% on the chart i9 w'hilethe latter :is -in motion.

In apracti'cal computer constructed in accordance with theinvention, the'following valuesmay be usedfor the elements of the adjustable voltage source for the recorder resistor 13:

Battery 25-6 volts Resistor '2-320 ohms Resistor 2'l--20 ohms Resistor lit-1,000 ohms Initially, the variable resistance "21 '(Fig. "1) 'is adjusted to'apply'to the recorder resistor 13a voltage such that when the pointer 48 (Fig?) is set at on the recorder scale 5!, the pen I"! will record the same percentage transmission as is indicated by the dial on the spectrophotometer l6. With the "blank cell in the 'light path or the spectrophotometer ill, initial wave length and slit-width settings are chosen an'd the'gain of 5. the amplifier [2 is adjusted to give a reading of 100% transmission.

In operation, the switch 23 is first thrown to the left. The recorder drive and the wave length drive of the spectrophotometer 10 are then start ed simultaneously. For best results, it is preferable to start the wave length drive at a value previous to those to be recorder and the recorder should be turned on when the starting wave length is reached. The recording of the blank transmission curve 5!] on the chart i9 is then allowed to proceed until the percentage transmission has decreased to approximately 50%. The wave length drive of the spectrophotometer Iii is then disengaged and is reset at its original value. At this time, the spectrophotometer l may be checked by means of the usual null indicator for drift which in most cases will be negligible.

' The recorder chart I9 is then rolled back to a wave length position slightly outside of the range L to be recorded. A recorder pen I! containing ink of a different color from that used to record the blank curve 59 is installed. The manually operated pointer 58 is then adjusted to the 100 position on the recorder chart scale and the switch 23 is thrown to the right. The calibrating variable resistance 21 is now adjusted until the recorder pen I! also indicates 160 on the scale 5!. The pen i! should now give the same reading for either position of the switch 23.

With the switch 23 thrown to the right and the sample cell in the light path of the spectrophotometer ill, the recorder ii is started simultaneously with the wave length drive at the same starting position on the chart l9 as was used for the blank curve 50. Meanwhile, the curve 50 for the blank cell is followed closely with the pointer 48 by manual operation of the adjusting knob 42. The recording pen I! then automatically traces a curve l8 which represents the percentage transmission for the sample alone.

The invention thus provides novel and highly effective apparatus for computing the percentage transmission of infrared radiation, or the like, through a sample. By manually adjusting the voltage applied to the resistor l3 in the recorder H, as a function of the blank transmission curve, while the sample transmission curve is being run, the desired percentage transmission curve for the sample alone can be obtained quickly and easily. Since only one curve must be followed manually, the apparatus is easy to operate and it is less expensive than computer apparatus of the type employed previously.

It will be understood that the invention is not limited to the determination of the percentage transmission of infrared radiation through a sample, as described in the specific embodiment illustrated herein. On the contrary, it may be employed generally for determining ratios between variables, or percentages, as will be apparent to those skilled in the art.

The specific embodiment disclosed herein is obviously susceptible of modification within the spirit of the invention, and it is not to be regarded as imposing any limitations whatsoever upon the scope of the following claims.

I claim:

1. In computer apparatus, the combination of a chart, means for moving said chart in one direction as a function of one variable, selfbalancing potentiometer means having an adjustable voltage divider the output voltage from which is balanced against a voltage representative of another variable, guide means providing ways extending in another direction, pointer means movably mounted on said ways and disposed so a to be moved to follow a recorded curve on said chart while the latter is in motion, a pair of spaced apart pulleys, a continuous belt mounted on said pulleys and connected to said pointer means for moving the same, sub-. stantially circular resistance means carried by one of said pulleys and engaged by a fixed contact, a source of electrical energy connected to the terminals of said resistance means, electric circuit means connecting said contact to said voltage divider for energizing the same, and means for recording a curve on said chart corresponding to the adjustment of said voltage divider.

2. In computer apparatus, the combination of a chart, means for moving said chart innone direction as a function of one variable, self-bal ancing potentiometer means having an adjustable voltage divider the output voltage from which is balanced against a voltage representative of another variable, guide means providing ways extending in another direction, pointer means movably mounted on said ways and disposed so as to be moved to follow a recorded curve on said chart while the latter is in motion, a pair of spaced apart pulleys, a continuous belt mounted on said pulleys and connected to said pointer means for moving the same, substan--. tially circular resistance means carried by one of said pulleys and engaged by a fixed contact, a source of electrical energy connected to the terminals of said resistance means, electric circuit means connecting said contact to said voltage divider for energizing the same, a second elec-, trical energy source of constant voltage, switching means for energizing said voltage divider selectively from said contact or from said second electrical energy source, and means for recording a curve on said chart corresponding to the adjustment of said voltage divider.

3. In computer apparatus, the combination of a chart, means for moving said chart in one direction as a function of one variable, electrical potentiometer means having a first adjustable voltage divider the output voltage from which is balanced against a voltage representative of a second variable, means operable by said potentiometer means for recording a curve on said chart representing the adjustment of said first voltage divider, pointer means movably mounted with respect to said chart, manually operable means for adjusting the position of said pointer means with respect to the chart, a second voltage divider means adjustable by said manually operable means, a source of electrical energy connected to said second voltage divider means, and electrical connections between said second voltage divider means and said first voltage divider for energizing the same.

4. In computer apparatus, the combination of a chart, means for moving said chart in one direction as a function of one variable, electrical potentiometer means having as a first adjustable voltage divider the output voltage from which is balanced against a voltage representative of another variable, means movable in another direction and operable by said first voltage divider for recording a curve on said chart, guide means providing ways extending in said another direction, pointer means movably mounted on said ways and disposed so as to be moved to follow a recorded curve on said chart while the latter is in motion, manually operable means for moving said pointer means along the ways, a second a sa e voltagerlivlder hav-ing.a2contact1ther eon,:a source of felectrical'zenergy.ifor said second voltage divider, ml'eans saetualtedliby' said manually operable means for producing relative engaging movement "between ("said Isecond voltage divider and the contact thereon, and-circuit means con.- necting .saidwontact'totsaidzfirst voltage divider tea-energize the latter.

5. inxcomputer apparatus, thezcombination 50f 'aschart having two coordinates, means Ifor :move me .said tch'ant .along' one 'fcoordinate zas Ia Tu-nee ti'on of-nn independent variable, pointer :means manuallyemovable along the :secondcoordinate,

'a ifirst voltage controllingmeans coupled .to said pointer means for producing a first voltagerepresenting'the position of the pointer :on said chart, a second voltage .controllingiimeans "for producing ra -second voltage proportional to :said first voltage, means for varying "the proportion of :said second "voltage to said first voltage to r substantially balance a voltage representing a with, :a second voltage divider having "a variable voltage from :saidflrstvoltag-e:divider impressed thereon, amotive means responsive to a voltage difference between the voltage 1 from said second voltage i divid'er -and la voltageurepresenting a dependent variable .quantityioriso adjusting :said second :voltagedivider as to. imaintain 'the voltage difference substantially at zero, andimeanscou vpled tosaidsecnnd voltage dividertforrecording a curve on saidchart asa function: of the position of said pointer means and the dependent variable.

7. .In computer apparatus, the combination of a :charthaving two coordinates, means for moving said chart along one coordinate as a function of an independent variable, pointer means manually movable along the second coordinate of said chart, a first voltage divider having a reference. potential impressed thereon and coupledto' said pointer means for adjustment therewith, 'a second voltage divider having a variable voltagerfrom .said first Voltage divider impressed thereoman amplifier having an input signal supplied 'thereto correspondingto the voltage from said second voltage divider and a voltagerepresenting a'dependent variable quantity, a motor responsiveito the amplitude and polarity of "the amplifier output signal "for so adiusting'saidfsecand voltage 'dividerthat the input si'gnal is.maintained substantially atzero, and means'couple'd to 'said second voltage divider for recording a curve on said char-t as a function of the position of said pointer means and the dependent variable.

WARREN JACKSON, :JR. ROBERT 'FOREMAN.

References 'Cited'in thefile of thisjpatent UNITED-STATES PATENTS Number Name Date 2,045,438 -Ciofii 'June 23, 1 936 2,212,799 Sperry Aug. 27, .1940 2,232,086 Van Den Akker d... Feb. 18, 1941 2,262,354 Oates Nov. 11, 1941 OTHER REFERENCES Publication Journal-Opticalsocietyof America, Sept. 1939, A mechanical integrator for evaluating the integral of the product of two func: tions and its application to the computationof .I. C. I. colorspecifications from spectrophotometric curves, by J. A. Van Den Ajkker, pages se l-s69. I 

